摘要
Most sedimentary formations with fine layers can be characterized as transversely isotropic media.The evaluation of shear-wave anisotropy is critical in logging-while-drilling(LWD)applications.We developed a joint method to simultaneously invert formation shear-wave anisotropy and vertical shear velocity using LWD monopole and dipole dispersion data.Theoretical analysis demonstrates that formation shear-wave anisotropy significantly aff ects the dispersion characteristics of Stoneley and formation flexural waves.The inversion objective function was constructed based on the change in dispersion characteristics and was weighted by the spectra of multipole waves.Numerical results using synthetic examples demonstrate that the joint inversion method can not only alleviate the non-uniqueness problem but also help improve the accuracy of the inversion results.The comparison of diff erent signal-to-noise ratio inversion results proved that the weighted inversion method is more accurate and stable.
大多数具有周期水平薄层构造的沉积地层可以表征为横向各向同性介质。在随钻测井中,为提高地层的横波速度和各向异性反演的可靠性与准确度,需要解决反问题中存在的非唯一性问题。为此本文提出了一种在随钻声波测井中利用单极斯通利波和偶极弯曲波的联合反演方法,同时获得地层横波各向异性和垂向横波速度。理论分析表明,斯通利波和地层弯曲波的频散特征都会受到地层横波各向异性的影响。利用其频散特征的改变我们构建了反演目标函数,并使用模式波的幅度谱对目标函数进行加权。通过对合成波形数据的处理证明联合反演方法不仅可以减少反演结果的非唯一性,而且有助于提高反演结果的准确性。通过不同信噪比数据反演结果的对比,验证了使用幅度谱加权的联合反演方法具有更高的反演精度和稳定性。
基金
supported by the National Natural Science Foundation of China (Grant No.12174421)
the Hubei Key Laboratory of Advanced Aerospace Propulsion Technology (Grant No.KFJJ2020-02).
